1. Field of the Invention
The present invention relates generally to devices for degassing liquids and, more particularly, but not by way of limitation, to devices for removing natural gas from drilling mud.
2. Brief Discussion of the Prior Art
It is a common practice in the drilling of an oil or gas well to circulate drilling mud through the well while drilling proceeds. The mud is stored in a mud pit from which it may be drawn for injection into the drill string and, after circulating through the bore of the well, the mud is returned to the mud pit.
The drilling mud serves several purposes; for example, lubrication of the drill bit and the removal of drill cuttings from the well. An important purpose served by passing drilling mud through the well is to maintain a hydrostatic pressure in lower portions of the bore to prevent the large scale release of natural gas, which can present a hazzard to drillers, into the well bore from porous formations that are penetrated by the drill. The hydrostatic pressure provided by the drilling mud is adjusted by varying the density of the mud to counter gas pressure in the formation so that the mud has the effect of sealing the intersection between the formation and the well bore. The result is that the mud limits the quantity of natural gas that can be released by the formation into the well bore.
In limiting the quantity of gas that is released into the well bore, the drilling mud will entrain some gas so that the fluid leaving the well is often in the form of a gas-drilling mud emulsion. The gas entrapped in the mud can give rise to various problems. For example, such gas can change the consistency of the mud sufficiently to interfere with the operation of pumps that are used to deliver the mud to the well and, more importantly, the gas can have a considerable, and undesirable, effect on the density of the mud. In particular, the gas-drilling mud emulsion can have a considerably lower density than the drilling mud alone with the result that the hydrostatic pressure in lower portions of the well bore can be decreased sufficiently to permit large quantities of gas to be released into the bore so as to give rise to the hazzards that the use of mud is, in part, designed to prevent.
It has, accordingly, become standard practice to degas the drilling mud after it has been returned from the well and prior to the reuse of the mud in the well. Several approaches have been taken to accomplish this degassing. In some devices, the mud is flowed over a plurality of baffles in an evacuated chamber as has been disclosed in U.S. Pat. No. 3,325,974 to Griffin III, et al. and in U.S. Pat. No. 3,898,061 to Brunato. Of course, it will be recognized that the use of a vacuum in these devices will increase both the cost of construction and operation of degassers of this type. Another approach has been to spray the mud in a diverging circular sheet at high velocity inside a chamber so that the impact of the mud with the walls of the chamber will cause separation of the gas from the mud. Devices of this type are manufactured by the Drilco Division of Smith International, Inc. of Oklahoma City, Okla. In the devices manufactured by Drilco, the mud is pumped from the mud pit into a riser pipe which has an upper end spaced a selected distance below a spray valve to turn the mud into a horizontal sheet which sprays out from the separation between such upper end of the riser pipe and spray valve to impact against the walls of a container wherein the valve is disposed. Such impact is used as a means for liberating gas from the mud. For best results, the distance between the upper end of the riser pipe and the spray valve is adjusted in relation to the rate of flow of the mud through the degasser.
While the prior art degassers have generally proven to be effective devices, they have also generally involved trade-offs between effectiveness and complexity of either construction or use. In general, it has not been possible, prior to the present invention, to provide a degasser which is simple in construction, easy to use and, at the same time, highly effective in the removal of natural gas from drilling mud.